In the recovery of hydrocarbon-containing fluid, such as oil, from hydrocarbon-bearing reservoirs, it is usually possible to recover only minor portions of the original oil by so-called primary recovery methods which utilise only the natural forces present in the reservoir. A variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean reservoirs. The most widely used supplemental recovery technique is water-flooding which involves the injection of water into the reservoir. As the water moves through the reservoir, it acts to displace or flush the oil therein towards a production well through which the oil is recovered. During recovery of hydrocarbon-containing fluid, reservoir pressure is thus maintained by injecting water from injection wells surrounding the production wells. The water cut of the recovered hydrocarbon-containing fluid is measured on a regular basis to detect water breakthrough. The water may come from the injection well or may be water which is naturally occurring from the reservoir. In order to avoid water breakthrough and enhance production, it has been attempted to use so-called second recovery methods using other drive fluids, such as CO2.
Another way of enhancing production of hydrocarbons in the recovered fluid is to use stimulation of the reservoir. The stimulation process comprises the use of tools and is rarely initiated before it is absolutely necessary, e.g. when the water cut is above a predetermined level, e.g. 90% water. Known stimulation tools send out mechanical vibrations into the reservoir when the water cut is decreasing or is above a predetermined level. The tool for emitting the vibrations is then submerged into the production well to the point approximately opposite the production zone while the production is set on hold. The production is then resumed after stimulation has been completed. Stimulation tools may also be arranged in the injection well so that production can continue during the stimulation process.